Polymerization of alkylene oxide in the presence of a complex catalyst (I) prepared by reacting an organoaluminum compound with a porphyrin compound of the formula (II) has been proposed (cf. Makromol. Chem., 182, 1073-1079 (1981)). ##STR1## wherein R.sup.1 is, the same or different, a hydrogen atom or a C.sub.1 -C.sub.4 alkyl group; R.sup.2 is, the same or different, a hydrogen atom or a C.sub.1 -C.sub.10 hydrocarbon group; and X is a hydrogen atom, a halogen atom or a C.sub.1 -C.sub.4 alkyl group.
In this method, alkylene oxide can be living polymerized by the use of the complex (I) according to the following reaction formula to give polyalkylene oxide having narrow distribution of molecular weight: ##STR2## wherein ##STR3## represents the complex (I), and n is a positive integer.
Since one mole of polyalkylene oxide is produced per mole of the complex (I) which is expensive, the produced polymer is fairly expensive.